一、字符串反转
把一个句子中的打次进行反转，比如“how are you” ,变为 “you are how”
// 字符串反转
public class StringTest {
// 字符反转的方法
private void swap(char[] c, int front, int end) {
if (front > end || end >= c.length) {
return;
}
while (front < end) {
char tmp = c[front];
c[front] = c[end];
c[end] = tmp;
front++;
end--;
}
}
// O(n)
public String swapStr(String str) {
char[] cArr = str.toCharArray();
// 整个字符串的字符反转
swap(cArr, 0, cArr.length - 1); // 反转整个字符串中的所有字母，how are you -> uoy era woh
int begin = 0;
// 对字符串中的每个单词反转，除了最后一单词
for (int i = 0; i < cArr.length; i++) {
if (cArr[i] == ‘ ‘) {
swap(cArr, begin, i - 1);
begin = i + 1;
}
}
// 最后一个单词的反转
swap(cArr, begin, cArr.length - 1);
return new String(cArr);
}
public static void main(String[] args) {
String str = "how are you";
System.out.println(new StringTest().swapStr(str));
}
}
二、判断字符串是否由相同的字符组成
判断连个字符串的字母个字母的个数是否一样，顺序可以不同， 如“aaaabc” 和“cbaaaa”是相同的
// 判断字符串是否由相同的字符组成
public class StringTest {
// 方法一 可以死任意字符 O(nlogn)
public boolean compareStr(String str1, String str2) {
byte[] bs1 = str1.getBytes();
byte[] bs2 = str2.getBytes();
Arrays.sort(bs1);
Arrays.sort(bs2);
str1 = new String(bs1);
str2 = new String(bs2);
if (str1.equals(str2)) {
return true;
} else {
return false;
}
}
// 只能是ASCII码 方法二 O(n)
public boolean compareStr2(String str1, String str2) {
byte[] bs1 = str1.getBytes();
byte[] bs2 = str2.getBytes();
int bCount[] = new int[256];
for (int i = 0; i < bs1.length; i++)
bCount[bs1[i] ]++;
for (int i = 0; i < bs2.length; i++)
bCount[bs2[i] ]--;
for (int i = 0; i < 256; i++) {
if (bCount[i] != 0) {
return false;
}
}
return true;
}
public static void main(String[] args) {
String str1 = "aaaabbc";
String str2 = "cbaaaab";
System.out.println(new StringTest().compareStr2(str1, str2));
}
}
三、字符串中单词的统计
给定一段空格分开的字符串，判断单词的个数
// 字符串中单词的统计
public class StringTest {
// O(n)
public int wordCount(String str) {
int word = 0;
int count = 0;
for (int i = 0; i < str.length(); i++) {
if (str.charAt(i) == ‘ ‘)
word = 0;
else if (word == 0 ) {
word = 1;
count++;
}
}
return count;
}
public static void main(String[] args) {
String str = "i am a good boy";
System.out.println(new StringTest().wordCount(str));
}
}
四、删除字符串中重复的字符
删除字符串中国重复的字符。如good -> god
// 删除字符串中重复的字符
public class StringTest {
// O(n^2)
public String removeDuplicate(String str) {
char[] cs = str.toCharArray();
int n = cs.length;
for (int i = 0; i < n; i++) {
if (cs[i] == ‘\0‘)
continue;
for (int j = i + 1; j < n; j++) {
if (cs[j] == ‘\0‘)
continue;
if (cs[i] == cs[j])
cs[j] = ‘\0‘;
}
}
int be = 0;
for (int i = 0; i < n; i++) {
if (cs[i] != ‘\0‘)
cs[be++] =cs[i];
}
return new String(cs, 0, be);
}
// 方法二： O(n)
public String removeDuplicate2(String str) {
char[] cs = str.toCharArray();
int n = cs.length;
int count[] = new int[256];
for (int i = 0; i < cs.length; i++) {
if (count[cs[i]] != 0)
cs[i] = ‘\0‘;
count[cs[i]]++;
}
int be = 0;
for (int i = 0; i < n; i++) {
if (cs[i] != ‘\0‘)
cs[be++] = cs[i];
}
return new String(cs, 0, be);
}
public static void main(String[] args) {
String str = "aaaabbc";
System.out.println(new StringTest().removeDuplicate(str));
}
}
五、按要求打印给定数组的排列情况
如1，2,2,3,4,5，要求第四位不为4,3和5不能相连
// 按要求打印数组的排列情况
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;
public class StringTest {
boolean visited[];
String combination = "";
int graph[][] = null;
public void getAllCombination(int arr[]) {
int n = arr.length;
graph = new int[n][n];
visited = new boolean[n];
buildGraph(arr, graph);
Set<String> set = new HashSet<>();
for (int i = 0; i < n; i++) {
depthFirstSearch(i, set, arr);
}
Iterator<String> iterator = set.iterator();
while (iterator.hasNext()) {
String string = (String) iterator.next();
System.out.println(string);
}
}
/**
* 按照深度优先遍历 图，将符合要求的组合加入到set中，自动去重
*
* @param start
* @param set
* @param arr
*/
private void depthFirstSearch(int start, Set<String> set, int arr[]) {
visited[start] = true;
combination += arr[start];
if (combination.length() == arr.length) {
if (combination.indexOf("4") != 2) {
set.add(combination);
}
}
for (int j = 0; j < arr.length; j++) {
if (graph[start][j] == 1 && visited[j] == false)
depthFirstSearch(j, set, arr);
}
// 什么意思?
combination = combination.substring(0, combination.length() - 1);
visited[start] = false;
}
/**
* 根据传入的数构建一个图，图中的 3,5 不能相连
*
* @param arr
* @param graph
* @return
*/
private int[][] buildGraph(int arr[], int[][] graph) {
for (int i = 0; i < arr.length; i++) {
for (int j = 0; j < arr.length; j++) {
if (arr[i] == arr[j])
graph[i][j] = 0;
else
graph[i][j] = 1;
}
}
graph[3][5] = 0;
graph[5][3] = 0;
return graph;
}
public static void main(String[] args) {
int arr[] = { 1, 2, 2, 3, 4, 5 };
new StringTest().getAllCombination(arr);
}
}
六、输出字符串的所有组合
给定一个字符串，输出该字符串中字符的所有组合
// 输出字符串的所有组合
public class StringTest {
public void combineRecursive(char[] c, int begin, int len, StringBuffer sb) {
if (len == 0) {
System.out.print(sb + " ");
return;
}
if (begin == c.length)
return;
sb.append(c[begin]);
combineRecursive(c, begin + 1, len - 1, sb);
sb.deleteCharAt(sb.length() - 1);
combineRecursive(c, begin + 1, len, sb);
}
public static void main(String[] args) {
String s = "abc";
char[] cs = s.toCharArray();
StringBuffer sb = new StringBuffer();
for (int j = 1; j < cs.length; j++) {
new StringTest().combineRecursive(cs, 0, j, sb);
}
}
}
原文地址：https://www.cnblogs.com/ytuan996/p/10679288.html
时间： 2024-10-15 22:01:56